1. Field of the Invention
The present invention relates to a moving object image tracking apparatus and method for enabling a target recognition sensor, such as a camera, to track a target that can move in every direction.
2. Description of the Related Art
In recent years, systems for tracking an object using, for example, an ITV camera, to realize continued monitoring or acquire detailed information have been produced on a commercial basis for protective service equipment employed in major facilities such as airports and manufacturing plants, lifeline facilities such as electric power plants and water networks, and traffic information support systems such as ITSs. These systems include not only ground equipment type systems, but also compact ones installed in vehicles, ships or airplanes and having a vibration-proof structure. In the systems, it has come to be important to enhance their whirling speed to make them quickly point a plurality of targets and sequentially track the targets.
It is necessary for the above moving object image tracking systems to incorporate at least two axes in its gimbal structure in order to track a target that can move in every direction. In biaxial gimbals, when a target passes the zenith or a position near the same, it is necessary to instantly rotate the AZ axis of the gimbal structure through 180°. Actually, however, this quick rotation is hard to execute, and hence the phenomenon, called gimbal lock, which makes it impossible to continuously track an object will easily occur. Therefore, the biaxial gimbal structure cannot be oriented to the zenith and its vicinity, which makes it difficult to realize omnidirectional tracking.
In light of the above, in some conventional image tracking systems, a triaxial gimbal structure is employed to enhance the degree of freedom in tracking, and is attempted to be used to continuously track a target in all directions, with its azimuth axis (Az axis) and cross elevation axis (xEL axis) controlled so as not to excessively increase the angular velocity to thereby avoid gimbal lock and make the movement of the gimbal fall within an allowable range (see, for example, JP-A 2006-106910 (KOKAI)).
In these conventional techniques, the gimbal structure is more complex than the biaxial one and requires another driving means (such as a motor), because the number of gimbals employed is larger by one than the latter structure. Thus, the triaxial gimbal structure is hard to reduce in size and cost. Further, in the triaxial gimbal structure, since a camera, for example, is installed, a great load inertia is applied to the xEL axis, which may cause interference between the Az axis and the xEL axis, which is a problem peculiar to the triaxial gimbal structure.
Further, to enable the biaxial gimbal structure to execute tracking near the zenith, a motor of such a performance capability as allows an instant 180° movement of each gimbal is required. This is an excessive imposition on the tracking apparatus.